On a Thursday in the small ring they run a couple of unaffiliated classes at 75cm & 85cm as warm ups before the 90Am then BN. TBH depends on who is building the course as to what you get. There is one course builder they use who imo does not build nice flowing courses, dont mind up to height if a course flows.
Good surfaces in both rings and the warm up, can be spooky as canteen and walkway right by the side of the arena.
Onley Grounds at near Rugby are also doing BSJA, they have intro shows with BSJA starting at 70cm and the courses there tend to be good, dont use the person I am refering to above, we tend to go there more now even though it is further to travel.
Be prepared for the rough driveway and carpark and at present portaloos, is all still a work in progress but the surfaces are excellent and the people very friendly and helpful.